The present invention relates to a Fabry-Perot interferometer, which can more particularly be used for spectrography or optical filtering.
A conventional Fabry-Perot interferometer comprises two parallel semi-transparent plates with a high reflection coefficient between which is formed an air gap having a strictly controlled thickness. An incident light ray supplies a series of emergent rays which interfere at infinity or in the focal plane of a lens. The interference fringes are bright rings on a dark background. In particular the centre is bright for a series of values of the ratio between the plate thickness and the wave length. By varying the thickness, e.g. by means of springs on which an action is exerted by screws, it is possible to modify at random the interference conditions.
This type of interferometer requires very fine settings, particularly with regard to the semi-transparent plates and the thickness adjustment. Technological considerations due to the mechanical regulating means conventionally used and problems concerning the overall dimensions limit the thickness of the air gap and consequently the wavelength resolution. Moreover, the thickness cannot be varied very rapidly.